1. Field of the Invention
The invention relates to a dry-type transformer with windings cast in casting resin and with at least one axial cooling canal provided in addition to the main leakage canal, preferably in the winding located radially outside the main leakage canal.
2. Description of the Prior Art
In the course of expansion and optimization of electric power distribution networks, it is frequently desired to increase the nominal voltage and/or the unit power rating of transformers. In many cases dry-type transformers are employed. Their unit rating and nominal voltage, however, have an upward limit. The reason for this is firstly because problems arise when removing heat from the core and the windings and secondly because the unit weights of the windings encapsulated by the casting resin as well as the casting resin body enclosing the windings are also subject to limitations for physical and technical reasons.
German Published, Prosecuted Application DE-AS No. 21 04 112 discloses a casting-resin insulated transformer winding with additional axial cooling canals located within the casting resin body. However, the manufacture of such casting-resin bodies enclosing windings is very costly from a production point of view. In addition, nothing substantial is changed in the practical operation between the unit weight of the casting resin body and the nominal power rating of the transformer in this conventional winding structure. In principle, nothing is changed as well if the winding is axially subdivided into several winding sections. For technically usable and sufficiently economical production of higher and higher nominal power ratings of casting resin transformers, farther-reaching solutions are therefore required.